Composite flexible armor

ABSTRACT

Layers of rigid platelets are separated by layers of compressible foam material having gas cells therein. A high velocity projectile striking a platelet in one layer compresses and forces gas from the cells in the foam material to absorb and dissipate kinetic energy.

E. BURGESS L COMPOSITE FLEXIBLE ARMOR May 28, 1974 Filed Jan. 30, 1975 ROW l ROWE FIGI.

FIG.3.

FIG. 2.

United States Patent 3,813,281 COMPOSITE FLEXIBLE ARMOR Lester E. Burgess, Swarthmore, and Ronald G. Brownstein, Broomall, Pa., assignors to Gulf Western Industrial Products Company, Salem, Ohio Filed Jan. 30, 1973, Ser. No. 328,100 Int. Cl. B32b 3/10, 5/20; F41h 1/02 U.S. Cl. 161-159 9 Claims ABSTRACT OF THE DISCLOSURE Layers of rigid platelets are separated by layers of compressible foam material having gas cells therein. A high velocity projectile striking a platelet in one layer compresses and forces gas from the cells in the foam material to absorb and dissipate kinetic energy.

BACKGROUND OF THE INVENTION This application relates to the art of energy absorption and dissipation, and more particularly to absorption and dissipation of kinetic energy from high velocity projectiles. The invention is particularly applicable to a flexible armor material for use in bulletproof vests or the like. However, it will be appreciated that the invention has broader applications and may be used for other purposes, such as lining vital parts of machinery or equipment for protection against damage from high velocity projectiles.

Armor material of known types for use in bulletproof vests or the like is too heavy, and lacks suflicient flexibility, to prevent discomfort when worn for long periods of time.

Flexible armor materials of known types commonly rely upon a cascading platelet principle. In such arrangements, a projectile strikes a platelet in a first platelet layer. The platelet struck by the projectile then bears against additional platelets in the next layer to spread the force of the projectile over a large area. In arrangements of this type, the rearward platelet layers usually require platelets of increasing size in order to insure that the force will be spread over a large area. The requirement for platelets of increasing area reduces the flexibility of the material.

Another flexible armor material of a known type includes a plurality of layers of platelets having elasto meric material layers interposed therebetween. A projectile striking a platelet causes compression of the clastomeric material to convert some of the kinetic energy to potential energy. Very little kinetic energy in the projectile is converted to potential energy by compressing dense elastomers or highly spongy elastomers.

Other flexible armor material of known types includes platelets of fiberglass reinforced plastic Which are intended to be penetrated by the projectile. Rupturing of such platelets dissipates some of the kinetic energy from the projectile.

SUMMARY OF THE INVENTION A composite flexible armor material for absorbing and dissipating kinetic energy from high velocity projectiles includes a plurality of layers of rigid platelets having compressible foam material interposed therebetween. The foam material is of the high density closed-cell or multicell type having very tight cells. When a projectile strikes a platelet in the outermost platelet layer, the platelet moves rearward to compress the foam material. Gas is compressed and forced from the cells in the foam material to absorb and dissipate energy from the projectile.

In accordance with a preferred arrangement, the platelets in each layer are individually secured to a substantially non-stretchable but highly flexible web member.

Patented May 28, 1974 Such a web member may be woven from nylon, fiberglass or metal yarn. When a projectile strikes a single platelet in the outermost platelet layer, rearward movement of the struck platelet carries adjacent platelets rearward because they are all attached to a substantially non-stretchable web member. This compresses the foam material over a very wide area so that a large number of gas cells have the gas forced therefrom to dissipate a substantial amount of kinetic energy from the projectile.

Compression of foam material in a first foam layer distributes force to platelets in a second platelet layer for compressing foam material rearward of the second platelet layer.

In accordance with a preferred arrangement, the foam material for the foam layers comprises a high density tight cell polyurethane plastic foam. The platelets in adjacent layers are also staggered relative to one another so that twisting of a platelet struck by a projectile will cause that struck platelet to impact against at least one additional platelet in a next platelet layer.

The use of a tight cell foam material minimizes the weight of the flexible armor material, while providing for dissipation of a substantial amount of kinetic energy by compressing and forcing gas from the cells in the foam material.

By flexibly interconnecting all of the platelets in each layer, and dissipating energy in forcing gas from the cells in the foam material, it is possible to make all of the platelets in each platelet layer of the same size. This greatly simplifies manufacture of the armor material and increases its flexibility.

In accordance with a preferred arrangement, each individual platelet in each platelet layer has a smoothly curved outer peripheral surface. Substantially rectangular platelets having sharp edges are more likely to tear the foam material. Circular platelets are one suitable shape. However, it will be recognized that other shapes are possible, including those having radial projections extending outwardly therefrom.

It is a principal object of the present invention to provide an improved flexible armor material.

It is another object of the present invention to provide a flexible armor material which is capable of dissipating kinetic energy from high velocity projectiles.

It is an additional object of the present invention to provide an armor material having a high degree of flexibility.

BRIEF DESCRIPTION OF THE DRAWING The invention may take form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawing which forms a part hereof.

FIG. 1 is a plan view of a flexible armor material constructed in accordance with the present invention;

FIG. 2 is a cross-sectional elevational view looking generally in the direction of arrows 2--2 of FIG. 1; and

FIG. 3 is a view similar to FIG. 2 showing how the armor material operates upon being impacted by a high velocity projectile.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, wherein the showings are for purposes of illustrating a preferred embodiment of the invention only and not for purposes of limiting same, FIG. 1 shows a composite flexible armor material A constructed in accordance with the present invention.

As shown in FIGS. 1 and 2, armor material A includes a first layer 12 formed from a plurality of individual rigid platelets 14. In a preferred arrangement, each individual platelet 14 is formed of steel having a thickness of around 0.005 to 0.01 inch. In the arrangement shown, each individual platelet 14 is circular and has a diameter between one and two inches. Depending upon the application to which the armor material will be put, it will be recognized that the size and thickness of each individual platelet may vary. In addition, it will be recognized that platelets having other than circular shapes may be used.

In accordance with one arrangement, platelets 14 in row 1 are positioned in contact with one another. Platelets 14 in row 2 are staggered one half of their diameter relative to the platelets in row 1 so that each platelet in row 2 contacts two platelets in row 1. Likewise, platelets 14 in row 3 are staggered one half of their diameter relative to the platelets in row 2. This staggered arrangement of the platelets in a single platelet layer greatly reduces the area of the open space between platelets.

Spaced rearwardly from first platelet layer 12 is a second platelet layer 16 having a plurality of platelets 18 which are dimensioned, shaped and positioned in the same manner as platelets 14 in first platelet layer 12. However, platelets 18 in second platelet layer 16 are staggered relative to platelets 14 in first layer 12 as shown in FIG. 1. Thus, platelets 18 in row 2 are staggered one half of their diameter relative to platelets 14 in row 1. Twisting movement of a platelet 14 in first platelet layer 12 will then insure that a platelet 18 in second platelet layer 16 will be forced rearward.

Spaced rearwardly of second platelet layer 16 is a third platelet layer 20 having individual platelets 22 therein which are dimensioned, shaped and positioned in the same manner as described with respect to platelets 14 in first 1 platelet layer 12. Platelets 22 in third platelet layer 20 are positioned so as to be immediately behind platelets 14 in first platelet layer 12. Thus, platelets 22 in third platelet layer 20 are staggered with respect to platelets 18 in the same manner as platelets 18 are staggered with respect to platelets 14.

In accordance with one arrangement, platelet layers 12, 16 and 20 are spaced-apart around A". Layers 26 and 28 of foam material are interposed between the platelet layers, and another layer 30 of foam material is located rearwardly of third platelet layer 20.

In accordance with a preferred arrangement, the individual platelets in each platelet layer are effectively connected with one another by a high strength substantially non-stretchable material which is highly flexible. This connecting material may be defined as a webbing which may take many forms. The interconnecting web may simply be strands of polyamide, glass or metal. Such a web may also be an open mesh fabric woven from such materials. In the arrangement shown, each platelet layer is secured to a web 36, 38 and 40. The web is preferably located on the rear surface of each platelet layer so that it faces the next platelet layer.

The individual platelets in each platelet layer are preferably adhesively secured to the webs. The webs and platelets are also preferably adhesively secured to the foam material. This will prevent adjacent layers from moving out of desired position relative to one another and prevent bunching of the foam material.

FIG. 3 shows operation of the device. A bullet 44 represents a high velocity projectile striking a platelet 14 in first platelet layer 12. Platelet 14 moves rearwardly to compress first layer 26 of foam material. Compression of first layer of foam material 26 compresses gas in the cells and forces gas from the cells to dissipate energy. Platelet 14 also cascades against a platelet 18 in second platelet layer 16. Platelet 18 then moves rearwardly to compress second foam layer 28. Compression of second foam layer 28 also transmits force to platelets 22 in third platelet layer 20 which move rearwardly to compress third foam material layer 30. With the arrangement described, it will be recognized that a plurality of layers of foam material are compressed, and that energy is dissipated by compressing and forcing gas from the cells in the foam material.

With the individual platelets in each layer bonded to a flexible and substantially non-stretchable web, rearward movement of an individual platelet 14 in first layer 12 also causes a plurality of adjacent platelets to move rearwardly. This causes compression of a substantial area of first foam material layer 26. Compression of this substantial area of first foam material layer 26 also causes rearward movement of a large number of platelets 18 in second platelet layer 16. Having platelets 18 connected to a web 28 of substantially non-stretchable material also causes compression and dissipation of energy over a large area in second foam material layer 28. Spreading of this force also occurs in third platelet layer 22 which is attached to third web 40.

It will be recognized that as many layers of platelets as required may be used. In addition, it will be recognized that the thickness of the armor material may be as large as necessary. In the preferred arrangement, each foam material layer 26, 28 and 30 is around A" so that the total thickness of material A is around It will be recognized that assembly of the armor material described may take place in a large number of different ways. For example, the platelets in each platelet layer may be positioned in their desired arrangement upon a fiat surface. Either the platelets themselves or the web may then be coated with adhesive. The web may then be placed in contact with the platelets. Slabs of foam material may then be adhesively secured to the webs and platelets, or foam material may be formed in-situ on the webs or platelets. A fabric material layer 50 may also be secured to the outer surface of first platelet layer 12. A layer of foam material may also form the outer surface for the armor material. It is also possible to adhesively secure the platelets to their respective webs and to then hang them in spaced-apart relationship in a mold. Foam material may then be introduced into the layers in a liquid condition so that it will foam and cure in the mold. The inherent adhesive nature of the foam material will then cause it to bond to the webs and platelets. When webs are not used, a layer of platelets may be positioned horizontally in a mold which is then filled with foam material.

The foam material will then bond to the platelets. A suitable rubber base adhesive may be used for bonding the platelets to the webs, and for bonding the foam material to the webs and platelets. The adhesive may be of the pressure-sensitive or hot melt type.

A preferred foam material for use in the armor material of the invention is a polyurethane cellular foam containing both open and closed cells. Foamed plastics in general, and polyurethane foam in particular, contain air or gas-filled cells distributed throughout the plastic material. These cells are formed in place by introduction of either chemical or solvent type blowing agents, as is well known in the art, and will therefore not be described in detail here. As is well known, it is possible to control the foaming action so as to obtain either closed or open cells or a combination of the two within the foamed material. Closed cells are pockets of air (or other gas) formed within the plastic material without outlets for the gas from the cell. Upon compression the gas contained within the cells is compressed as the cell is deformed, and expands as the pressure is relieved and the cell returns to its original shape.

Open cells are cells which contain an opening or window leading from the cell wall to interstices within the plastic material itself. Upon compression of the material the cell is distorted and the air or gas contained within the cell is compressed and escapes through the window into interstices within the foam material. Impact energy is thus absorbed both by compression of gas trapped within the closed cell and by the compression and expulsion from the foam of gas contained within the open cells. The combination of spring-type action provided by the closed cells and air expulsion action through the small interstices of the foam provided by the open cells, has been found to be highly advantageous with respect to the shock absorbing characteristics of the foamed material.

A high density polyurethane foam plastic, i.e., a foamed polyurethane with a material density of over 7 lbs. per cubic foot (preferably between about 10 and about lbs. per cubic foot) has been found to be an outstanding shock absorbing material for use in the armor material of the invention. A tight foam with between about 90 to about 99% of the cells being of the open type and the remainder being of the closed type has been found to be particularly advantageous because the high rate of air flow through the restricted openings in the foam provides a built-in shock absorber elfect. It has been found that with a tight foam, the faster the rate of loading, the more resistance there is to the expulsion of air from the foam, and the greater is the shock absorbing capacity of the material. This provides a material particularly well suited for use as a shock absorbing material for armor material. The impact of a projectile represents an extremely high rate of loading. It is to be understood that the high density, tight cellular foam is preferred for use with any and all embodiments of the invention.

Although the invention has been shown and described with respect to a preferred embodiment, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications and is limited only by the scope of the claims.

Having thus described our invention, we claim:

1. A composite flexible armor material for absorbing and dissipating kinetic energy from high velocity projectiles comprising; at least one layer of compressible foam material having gas cells therein, at least one layer of rigid platelets attached to said layer of compressible foam material, said layer of rigid platelets including a plurality of individual platelet members, said platelets being operative upon being struck by a projectile to compress said foam material by compressing gas in said cells and forcing gas from said cells for absorbing and dissipating energy from the projectile.

2. The armor material of claim 1 wherein said platelet members are individually secured to a substantially nonstretchable flexible web member whereby compressing movement of one of said platelets upon being struck by a projectile is transferred by said web to adjacent other platelets so that said web and adjacent platelets also compress said foam material to absorb and dissipate energy from the projectile.

3'. The armor material of claim 1 wherein there are a plurality of said layers of foam material and a plurality of said layers of platelets, including a first impact platelet layer and a second platelet layer located between said layers of foam material and spaced from said first platelet layer by one of said layers of foam material, whereby a projectile striking one of said platelets in said first platelet layer causes said one platelet to move and compress said one layer of foam material for absorbing and dissipating energy and transfers force from said one platelet to additional platelets in said second platelet layer so that said additional platelets move to compress the other of said layers of foam material for absorbing and dissipating energy,

4. The armor material of claim 3 wherein said platelets in each of said platelet layers are secured to a web of substantially incompressible non-stretchable flexible material.

5. The armor material of claim 3 wherein each of said platelets in said second platelet layer are staggered relative to each of said platelets in said first layer.

6. The armor material of claim 5 wherein said platelets in said first platelet layer are of substantially the same size as said platelets in said second platelet layer.

7. The armor material of claim 4 wherein each of said platelets in said second platelet layer are staggered relative to each of said platelets in said first layer.

8. The armor material of claim 3 wherein each of said platelets in said second platelet layer are staggered relative to each of said platelets in said first layer.

9. The armor material of claim 1 wherein said foam material comprises a high density tight cell polyurethane plastic foam.

References Cited UNITED STATES PATENTS 2,723,214 11/1955 Meyer 161-404 3,563,836 2/ 1971 Dunbar 161--404 3,577,836 5/1971 T amura 16l404 WILLIAM J. VAN BALEN, Primary Examiner U.S. Cl. X.R. 

